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Change of Ms Temperatures and its Correlation to Atomic Configurations of Offstoichiometric NiTi-Cr and NiTi-Co Alloys

Published online by Cambridge University Press:  10 February 2011

Hideki Hosoda ,
Toshihiko Fukul ,
Kanryu Inoue ,
Yoshlnao Mishima  and
Tomoo Suzuki
Hideki Hosoda
Affiliation:
Now wilh Institute for Materials, Tohoku University, 2–1–1 Katahira, Aoba-ku, Sendai 980–77, Japan.
Toshihiko Fukul
Affiliation:
Now with NKK Cooperation, Minamiwatarida, Kawasaki-ku, Kawasaki 210, Japan
Kanryu Inoue
Affiliation:
Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195–2120, USA
Yoshlnao Mishima
Affiliation:
Precision and Intelligence Laboratory, Tokyo Institute of Technology, 4249 Nagatsuta, Midori-ku, Yokohama 226, Japan
Tomoo Suzuki
Affiliation:
Professor Emeritus, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152, Japan.
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Abstract

Effects of compositional deviation from the stoichiometry and Cr and Co additions on martensitic-transformation-slart and auslenite-start temperatures (Ms and As) of offstoichiometric NiTi alloys are investigated. Ms and As are determined using conventional differential thermal analysis (DTA), where the temperature range investigated is between 77K and 423K. Alloys are widely chosen with both Ni- and Ti-rich compositions, to which ternary elements, Cr and Co, are added. It is clearly shown that Ms and As in single phase regions are reduced with increasing amount of constituent element, Ni, and ternary elements, Cr and Co. On the other hand, Ms and As do not depend on Ti concentration when Ti concentration is more than 52mol.%. NiTi alloys are in two phase region in the case. Ms changes by Co at offstoichiometry are evaluated to be -15K / mol.% in Ni poor side and -30K / mol.% in Ni rich side. These values correspond to -22K / mol.% for the stoichiometric NiTi alloys. Also, effects of Cr on Ms are evaluated to be -65K / mol.% in Ni poor side and -45K / mol.% in Ni rich side. The former is similar to the Ms change in stoichiometric alloys, and the latter is close to our prediction of -30K / mol.% in comparison with the reported value of -120K / mol.% for stoichiometric alloys. It is concluded for offstoichiometric NiTi alloys that effects of ternary additions on Ms can be explained using electronic structures of ternary elements by taking atomic configurations into account, as well as the stoichiometric NiTi alloys. Effect of degree of order is also discussed.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 459: Symposium Y – Materials for Smart Systems II , 1996 , 287
Copyright
Copyright © Materials Research Society 1997

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References

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